The invention relates in general to the area of wireless communication with at least one mobile subscriber via a communication channel with varying availability. In particular, the invention relates to a data transmission method as well as an associated data transmission unit, which are improved with regard to the reliability of the data transmission, wherein reliability requirements of services and applications can in particular be taken into account.
On account of its flexibility, cost efficiency and mobility support, wireless data transmission has a broad range of applications beyond conventional mobile communication. Several examples of application are road traffic safety technology, rail traffic control systems, industrial applications and e-health applications. Many applications and services are dependent on the reliability of the data transmission, i.e. the successful and prompt transmission of information. For example, it is necessary in the case of road traffic safety applications based on wireless data transmission that a very high percentage of safety alerts is correctly transmitted within a specific time interval (see Intelligent Transport Systems (ITS); Vehicular Communications; Basic Set of Applications; Definitions, ETSI Technical Report TR 102 638 Rev. 1.1.1, 2009.) Safety alerts that are not delivered or are delivered incorrectly represent a high risk potential.
On the other hand, a wireless data transmission system cannot be designed in practice such that it can ensure a reliable data link at all times and under all circumstances, since such a system would be inefficient and/or associated with high energy consumption.
Various methods are already used in known wireless communication systems to compensate for fluctuations in the transmission quality of the communication channel and to ensure a minimum of reliability of the data transmission for services and applications. Examples of this are the hybrid automatic repeat request (HARQ) and the adaptive modulation and coding (AMC), such as are described for example in A. J. Goldsmith et al., “Adaptive coded modulation for fading channels”, IEEE Transactions on Wireless Communications, vol. 46, no. 5, pp. 595-602, May 1998, or in “Physical layer procedures (Release 8)”, 3GPP technical specification 36.213 for cellular communication systems, such as for example the 3GPP LTE (Long Term Evolution, LTE).
HARQ is based on the combination of forward error correction (FEC) and repeated transmission of data unusable at the receiver side and is split up into HARQ-type-I and HARQ-type-II. In the case of HARQ-type-I (also plain automatic repeat request, ARQ), erroneous packets are simply deleted and retransmitted. In the case of HARQ-type-II (also HARQ with incremental redundancy, IR-HARQ), an attempt is made to combine the erroneous data transmitted in various repeated transmissions. The probability of a successful transmission is thus increased. HARQ and AMC or other known measures cannot guarantee an error-free and prompt data transmission, i.e. ensure the latter with 100% probability, in cellular communication systems on account of the random fluctuations of the transmission quality of the wireless communication channel.
In the case of data transmission, however, services such as road traffic safety applications require a very high and predictable success rate (e.g. 99.999%) with very short maximum time intervals (e.g. 10 ms) within which the data transmission must take place. It has therefore already been proposed to inform a service or an application, which requires a reliable data transmission, as to the availability or non-availability of a reliable data transmission link. A data transmission method and an associated data transmission unit for the provision of a reliable communication channel for a real-time application is proposed for example in as yet unpublished German patent application DE 10 2013 221 649.1 of the same applicant, wherein the availability of a reliable communication channel is predicted and indicated by means of an availability indicator. The data transmission concept of DE 10 2013 221 649.1 is based on the idea of ascertaining, before the transmission of data, a probability of availability of the communication channel and of transmitting data only when there is sufficient probability of availability. That is to say that a data transmission should only take place when the probability of data transmission errors is very low or approaches zero.
Time interval-dependent coding (deadline dependent coding, DDC), such as is described for example in E. Uhlemann et al., “Deadline dependent coding—a framework for wireless real-time communication”, International Conference on Real-Time Computing Systems and Applications”, December 2000, pp. 135-142, is a kind of HARQ. In the case of DDC, an attempt is made to meet real-time requirements by means of a data transmission with a specific probability PDL before the lapse of a time interval td. For this purpose, the code rate and the number of transmission repetitions are calculated a priori, such that reliability-relevant parameters td and PDL can be achieved.
Especially services for and applications with safety-relevant functions have high reliability requirements on data transmission links. The reliability requirements are defined here as the successful transmission of data to be transmitted within a specific time interval with a specific probability. Present cellular communication systems do not at present take account of such reliability requirements of services and applications in order to configure the data transmission. This limits the possibilities especially of a cellular communication system to guarantee reliability, and at the same time reduces its efficiency.
In the prior art, such as for example in the aforementioned DDC, reliability requirements of services and applications with regard to the time interval and the probability of a correct data transmission before the lapse of the time interval are only taken into account for the purpose of configuring the size of transmission blocks and the number of transmission repetitions. In the case of DDC, the configuration is calculated a priori, wherein an average is taken over all possible communication channel parameters. It is not therefore possible to adapt the DDC to temporal fluctuations of the transmission properties of the communication channel in real time.
It is the problem of the present invention to specify a data transmission method which is improved in respect to the reliability of the data transmission, in particular with regard to taking account of reliability requirements of real-time services and applications. Furthermore, a corresponding data transmission unit is to be provided, which is configured in particular for the provision of a reliable communication channel for a real-time application or a real-time service. Moreover, a vehicle with a corresponding data transmission unit is to be specified.
A core idea of the invention lies in the concept of integrating the availability indication of a communication channel into a data transmission method based on the HARQ concept, such as for example the DDC. The data transmission method in this case takes account of predetermined reliability requirements of the application or service using the communication channel in the or for the configuration of the data transmission. As a result, the reliability of the data transmission for the service or application is improved on the one hand, but also the efficiency of the overall system.
A first aspect of the invention relates to a method for the data transmission at a transmitter-side data transmission unit comprising the steps:
a) receiving a data transmission request for a data packet from a real-time application which is operatively connected to the data transmission unit;
b) transmitting a first portion of the data packet to a receiver-side data transmission unit via a communication channel;
c) receiving an availability indicator for the communication channel from the receiver-side data transmission unit; and
d) if the availability indicator shows that the communication channel is available, configuring the data of the data packet yet to be transmitted for a successful transmission within the still available time of a maximum permissible data transmission time determined by the real-time application for the data packet, and transmitting the data packet.
In step a), information concerning the amount of data and/or the maximum permissible data transmission time and/or a maximum permissible transmission error rate can be transmitted from the real-time application to the transmitter-side data transmission unit. These boundary condition data can also be transmitted with the one first portion of the data packet to the receiver-side data transmission unit and/or can be pre-configured in the receiver-side data transmission unit and/or can be stored retrievably in a central database (a server) of the communication system.
The transmission of the first portion of the data packet serves as a basis for the receiver-side prediction of the availability of the communication channel for the current transmission horizon. The current transmission horizon is understood here to mean the difference arising from the maximum permissible data transfer time for the data packet less the already elapsed time for one or, as the case may be, more (yet to be explained) transmissions of the first portion that have already taken place plus any pauses etc. within the current data transmission time.
The first portion of the data packet serves as a basis for a receiver-side measurement of parameters (relevant for the transmission reliability) of the communication channel for predicting the availability of the communication channel.
The length of the first portion of the data packet can be determined by setting a specific number of information symbols and/or timeslots. The length of the first portion can be determined in particular with regard to the current transmission horizon and the time variance of the parameters of the communication channel. The first portion is preferably set short in the case of very rapidly fluctuating parameters of the communication channel. The first portion is preferably set long in the case of slowly fluctuating parameters of the communication channel. The length of the first portion is preferably determined on the basis of the coherence time of the communication channel. The length of the first portion is not therefore dependent on the maximum permissible data transmission time. In general, it is recommended, in the case of a very rapidly fluctuating communication channel (e.g. when travelling at high speed), to provide the length of the first portion with several milliseconds (ms). In the case of a slowly fluctuating communication channel (e.g. when travelling at lower speed), on the other hand, the length of the first portion can amount to several hundred ms.
The coherence time of the communication channel is understood here to mean the time interval within which the coefficients of the impulse response of the communication channel can be assumed to be constant.
The method can also comprise the following steps:
e) if the availability indicator shows that the communication channel is not available, termination of the transmission of the data packet; and
f) after a predetermined pause, repetition of the method from step b), if sufficient time for the transmission of the data packet is still available up to the lapse of the maximum permissible data transmission time for the data packet, i.e. up to the current transmission horizon.
The configuration of the data of the data packet yet to be transmitted for a successful transmission within the still available time of a maximum permissible data transmission time determined by the real-time application for the data packet includes in step iv): adjustment of the number and length of data blocks of the data packet yet to be transmitted taking account of transmission repetitions of individual data blocks that are to be expected.
The transmitter-side data transmission unit can, if it has been ascertained that the communication channel is not available, terminate a data transmission link to the associated receiver-side data transmission units and release the assigned communication channel for use by another data transmission units. This can preferably be implemented already on or in the physical (PHY) and/or Medium Access Control (MAC) layer of the transmission protocol used. An opportunistic allocation of subscribers to communication channels of a communication system can thus be achieved based on the availability of the communication channel ascertained at the time. This is particularly advantageous for the efficiency of communication systems with a plurality of subscribers (multi-user system), in which different messages are to be transmitted to different subscribers in the coverage range of the communication system. The transmitter-side data transmission unit can for example be a base station of a mobile radio system and can be set up to assign communication channels, as a limited radio resource of the mobile radio system, only to those subscribers for whom a positive availability has been established according to the reliability requirements of the application or service of the communication channel using said communication channel. In other words, for those subscribers for whom the availability of the communication channel has been determined as not available, an initiated data transmission is stopped until more favorable communication channel properties are available, i.e. the communication channel is available according to the criteria defined here.
A second aspect of the invention relates to a method for data transmission at a receiver-side data transmission unit comprising the steps:
i) receiving a first portion of a data packet from a transmitter-side data transmission unit via a communication channel;
ii) determining an availability indicator for the availability of the communication channel on the basis of parameters of the communication channel measured during the reception of the first portion of the data packet and on the basis of the predicted parameters of the communication channel for the still available remainder of a predetermined maximum permissible data transmission time for the transmission of the data packet;iii) transmitting of the determined availability indicator to the transmitter-side data transmission unit;iv) receiving the remaining data packet if the determined availability indicator shows that the communication channel is available.
The determination of the availability of the communication channel in step b) preferably takes place on the basis of parameters of the communication channel measured during the transmission of the first portion of the data packet and predicted for the remaining period up to the current transmission horizon.
The parameters for the communication channel can be one of or a combination of the following: an ACK statistic, a NACK statistic, SINR values, fluctuation values in respect of the communication channel in the time range, coherence times of the communication channel, an amount of an intercarrier interference in an orthogonal frequency multiplex system (OFDM), a Doppler frequency, CQI values, RSSI values, RSRQ values, RSCP values, MIMO-Rank values, Ec/Io value, QCI value.
With regard to the aforementioned parameters, reference should be made to the following brief explanations:
ACK (ACKnowledge) describes a signal for confirming a data transmission.
NACK (Not ACKnowledged) describes the rejection of transmitted data and its acknowledgement.
SINR (Signal-to-Interference-and-Noise-Ratio) is the signal-to-noise ratio.
CQI (Channel Quality Indicator, CQI) is a measurement value for the communication quality of a wireless communication channel.
RSSI (Received Signal Strengths Indicator) is an indicator of the reception field strength of a wireless communication channel.
RSRQ (Reference Signal Received Quality) is a calculated ratio which results from the value for RSRP and the RSSI; the RSRQ serves to assess an LTE link or the reception quality of the mobile terminals.
RSCP (Received Signal Code Power) describes the power measured at the receiver of a communication channel.
Ec/Io indicates the ratio of the average power of the communication channel to the total signal strength.
MIMO-Rank (Multiple-Input-and-Multiple-Output Rank) denotes in communication engineering the use of a plurality of transmission and reception antennas for wireless communication, wherein Rank describes the ratio to one another.
QCI (Quality Class Indicator) is used in LTE technology to split up different applications with different “packets delay budgets” and “packet error loss rates”.
Step iv) can also comprise: 1) calculating a value for the accumulated mutual information content (ACcumulated Mutual Information, ACMI) after each transmission repetition of a data block of the data packet and 2) comparing the calculated ACMI value with the ACMI value according to the estimated parameters for the communication channel; and 3) transmitting an adapted data block size to the transmitter-side data transmission unit to compensate for deviations between the calculated ACMI value and the estimated ACMI value. It is thus possible to compensate for prediction errors in the parameters for the communication channel that have a negative influence on the configuration of the data of the data packet yet to be transmitted for a successful transmission within the still available time up to the current transmission horizon.
A third aspect of the invention relates to a transmitter-side data transmission unit for providing a communication channel for a real-time application, wherein the data transmission unit comprises: at least one data output/reception unit, at least one availability determination unit for determining the availability of a communication channel between the data output/reception unit of the data transmission unit and at least one receiver-side data transmission unit, wherein the availability determination unit is set up to perform a method according to the first aspect of the invention.
A fourth aspect of the invention relates to a receiver-side data transmission unit for providing a communication channel for a real-time application, wherein the receiver-side data transmission unit comprises: at least one data output/reception unit, at least one availability determination unit for determining the availability of a communication channel between the data output/reception unit of the data transmission unit and at least one transmitter-side data transmission unit, wherein the availability determination unit is set up to perform a method according to the second aspect of the invention.
It should be noted that a data transmission unit can be configured both as a transmitter-side data transmission unit according to the third aspect and also as a receiver-side data transmission unit according to the fourth aspect. That is to say that such a data transmission unit can perform both the role of the transmitting data transmission unit and also of the receiving data transmission unit.
A further aspect of the invention thus relates to a data transmission unit for providing a communication channel for a real-time application, wherein the data transmission unit comprises: at least one data output/reception unit, at least one availability determination unit for determining the availability of a communication channel between the data output/reception unit of the data transmission unit and at least one transmitter-side data transmission unit, wherein the availability determination unit is set up to perform the method according to the first and the second aspect of the invention.
The data transmission unit of the third, fourth and further aspect of the invention can also comprise: an availability output unit, which is configured for outputting the availability indicator, and/or a data transmission request unit, which is configured for triggering an availability request to the availability determination unit.
The data transmission unit of the fourth and further aspect of the invention preferably comprises, for its receiver-side role, one or more detection units for detecting at least one of the aforementioned parameters of the communication channel, which detection unit is set up to transmit the detected or measured parameter data to the availability determination unit. The data ascertained by the unit or the units for monitoring the communication channel parameters are sent or transmitted to the availability determination unit, so that the availability of the communication channel can be determined inter alia depending on these parameters.
A fifth aspect of the invention relates to a data communication system with at least one transmitter-side data transmission unit according to the third or further aspect of the invention and a receiver-side data transmission unit according to the fourth or further aspect of the invention.
The data transmission units preferably serve to provide a communication channel for a real-time application. The communication channel is preferably constituted between a transmitter-side data transmission unit according to the invention and at least one further receiver-side data transmission unit.
The receiver-side and/or transmitter-side data transmission unit can also be a base station of a communication network, so that a data transmission or the provision of a communication channel for a real-time application between a data transmission unit according to the invention and a further data transmission unit can take place via the communication network. The data transmission units can also each be regarded and constituted as devices and can comprise corresponding device features such as for example electrical components, an electronic circuit, a microprocessor for processing commands of a computer program and so forth, so that a method sequence according to the invention is implemented in each case.
The interaction of the method for the data transmission to a transmitter-side data transmission unit with the method for the data transmission to a receiver-side data transmission unit is explained below by way of example.
At a time ti, a message mi concerning J transmission blocks with a length of τij timeslots (it should be assumed in the example that the duration of each timeslot corresponds to the time duration for the transmission of one bit), i.e. τij∈N and j=1, . . . , J with a maximum transmission time T required by the real-time application, is to be transmitted to the transmitter-side data transmission unit, wherein Σjτij≤T applies. After reception of the transmitted transmission blocks over a first number ωi of timeslots, a parameter relevant to the availability of the communication channel, for example the signal-to-noise ratio SINR for the following T−ωi timeslots up to maximum transmission time T, is predicted or estimated at the receiver-side data transmission unit. The prediction can take place for example by means of a linear extrapolation, such as is explained for example in M. Ni et al., “A channel feedback model with robust SINR prediction LTE systems”, IEEE European Conference on Antenna and Propagation, EuCAP, pages 1866-1870, 2013.
On the basis of the parameter (e.g. SINR) measured for the communication channel during the first timeslots ωi and parameter values (e.g. SINR) predicted for the following timeslots T−ωi, the receiver-side data transmission unit determines the availability of the communication channel, i.e. whether the communication channel is sufficiently reliable. The availability thus determined is communicated by the receiver-side data transmission unit to the transmitter-side data transmission unit by means of the availability indicator.
If the communication channel has been determined as sufficiently reliable, i.e. the latter is classified as available, the data transmission of the message can be continued up to the end of the transmission block. Otherwise, if the communication channel has been determined as not sufficiently reliable, i.e. the latter is classified as not available, the data transmission can be terminated. The data already received up to then at the receiver-side data transmission unit up to time ti+ωi, which are present for example in a receive buffer memory, are discarded.
As already described above, the transmitter-side data transmission unit can repeat the transmitter-side process after a predetermined pause δ, as long as sufficient time is still available up to the lapse of the maximum permissible transmission time T. The receiver-side data transmission device will then also re-determine, always after the transmission of the first ωi bit, the availability of the communication channel, as described above, as long as sufficient time is still available for the transmission of the data packet, i.e.
                              ∑                      j            =            1                    J                ⁢                  τ          ij                    +                        (                      J            -            1                    )                ⁢        ϑ              ≤          T      -              n        ⁡                  (                                    ω              i                        +            δ                    )                      ,wherein ϑ is a runtime delay between successive transmission blocks, and n is the counter to establish how often the communication channel has been classified as not available, i.e. not sufficiently reliable.
A sixth aspect of the invention relates to a vehicle with a transmitter-side data transmission unit according to the third aspect of the invention and/or a receiver-side data transmission unit according to the fourth aspect of the invention or a data transmission unit according to the further aspect of the invention.
The vehicle preferably comprises a processor which implements the real-time application, in particular a driver-assistance functionality, such as for example a brake assist system. Similar advantages arise as those that have already been described in connection with the transmitter-side and receiver-side data transmission unit.
When the real-time application implements a driver-assistance functionality, the data transmission unit of the vehicle can be connected to at least one sensor for determining a vehicle parameter under operating conditions for transmitting sensor data to the availability determination unit. The sensor can be set up to determine the vehicle speed and/or to determine the direction of travel and/or to determine the distance from an obstacle. The sensor can be at least one camera and/or a radar system and/or a LIDAR system.
The determination of the availability of the communication channel in step c) of the method according to the second aspect can take place depending on vehicle parameters, in particular depending on a vehicle speed and/or a direction of travel of the vehicle and/or positional data of the vehicle and/or a distance from another vehicle.
The availability of the communication channel can be indicated to a driver of the vehicle in a display unit of the vehicle, preferably by means of a symbol in a driver information system, for example in an instrument cluster or a head-up display. The display of the availability indicator can take place as an absolute display, i.e. a display can take place as to whether a communication channel is available or not. In this connection, a distinction needs to be made solely between two display symbols. If the display unit for indicating the availability of the communication channel indicates for example no availability of the communication channel, the driver can conclude from this that his vehicle cannot establish a connection or a communication with other vehicles. For example, this may mean that a brake assist system of the vehicle cannot receive the signals of a vehicle travelling in front. The driver is thus informed that the brake assist system is possibly not automatically engaging, so that the driver is required to maintain a raised state of awareness. The lack of availability of a communication channel may also mean that a data link to a service which runs on a back-end server, which can be reached via a base station of a communication network, cannot be established. Such a service may for example be an information service for the current traffic situation. With the lack of a data link, the driver knows that the traffic situation data used in his navigation system are not up to date or are not present and traffic jams are not therefore avoided etc.
The driver assistance functionality can for example be set up, on the basis of the availability of the communication channel, to make a decision to initiate a driver assistance measure, in particular to initiate a steering intervention and/or a vehicle acceleration and/or a braking action and/or a speed reduction in a first mode and/or a second mode. The driver assistance functionality is preferably operated in the first mode as a function of data received from the communication channel and in the second mode as a function of data of the at least one sensor for determining a vehicle parameter. A switch from the first mode into the second mode and vice versa preferably takes place depending on the availability of the communication channel.
It should be noted that the data transmission unit can in principle be a mobile communication device, e.g. a cellular telephone, but also an on-board computer of a vehicle with corresponding communication interfaces.
The data output/data reception unit may be a close-range radio unit, such as for example a Wi-Fi unit and/or a Bluetooth unit and/or a ZigBee unit, but also in addition or alternatively a mobile radio unit. As a mobile radio unit, the latter can be based for example on a 3GPP standard, such as the LTE standard or a future mobile radio standard, such as for example the 5G standard. The data output/data reception unit can of course be based, alternatively or in addition, on another communication standard for wireless communication, such as for example the 802.11p or a future standard.
Moreover, it should be noted that, insofar as the data transmission unit is implemented not in a vehicle, but other systems or units, the real-time application can for example be automatic rail traffic control systems, e-health services and comparable industrial applications.
Finally, it should be noted that the methods and data transmission units according to the invention can be used not only in automotive applications, but also on all other wireless transmission systems or applications. This applies both to wireless communication systems which are based on a direct device-to-device communication, such as for example the standard 802.11p, or on an infrastructure-based communication, such as for example 3GPP LTE.
Further objects, advantages, features and details of the invention emerge from the following description, in which an embodiment of the invention is described in detail making reference to the drawings. The features mentioned in the claims and in the description here can be essential to the invention in each case individually in themselves or in any combination. The aforementioned features and the further features mentioned here can likewise each be used in themselves or in a plurality thereof in any combinations. Identical components or components with similar functions are in part provided with identical reference numbers. The terms “left”, “right”, “above” and “below” used in the description of the embodiments relate to the drawings in an orientation such that the reference numbers and names of the figures can be read normally. The embodiment shown and described is not to be understood as conclusive, but is in the nature of an example to explain the invention. The description serves to inform the person skilled in the art, so that known circuits, structures and methods are not shown or explained in detail in the description in order not to make the understanding more difficult.